Loudspeaker box for a preferably dynamic loudspeaker

ABSTRACT

A cabinet for a loudspeaker, preferably a dynamic loudspeaker, comprises a front wall, a rear wall and a plurality of side walls. A loudspeaker is mounted on a partition which is arranged behind the front wall and which is spaced from the front wall so as to define an annular gap which surrounds the rims of sound apertures defined by the front wall and the partition. Bracing means brace at least one pair of opposite walls of the cabinet and foam material defining at least one damping wall is disposed within the cabinet, to damp standing waves.

[is] 3,680,658 [4 Aug. 1,1972

United States Patent Goeskel [s41 LOUDSPEAKER Bork FOR A 2,900,040 8/1959 Novak.. PREFERABLY DYNAMIC 3,082,839 3/ 1963 Whitcas LOUDSPEAKER 3,104,730 9/1963 Brown.. 3,135,349 6 1964 L ht'.... [72] Inventor: Helmut Goeskel, Liebenau/Weser, 3,247,926 441966 fi g Germany 3,412,824 1 1/1968 Armstrong [73] Assignee: Neckermann Versand KGaA, Frank- Primary Examiner-Stephen J. Tomsky Attorney-Lewis H. Eslin Curtis, Morris & Safl'ord furt, Main, Germany May 10, 1971 ger, Alvin Sinderbrand and [22] Filed:

ABSTRACT [21] Appl. No.: 141,665

standing waves.

UNITED STATES PATENTS 2,694,463 11/1954 Robbins et 181/31 B 28 Claims, 7 Drawing Figures PATENTEDAus 11912 I 3.680.658

SHEET 2 UF 2 FIGA BY 1 6% a BEST AVAILABLE COPY 3,680,658 a 1 2 LOUDSPEAKER BOX FORAPREFERABLY ter. Nevertheless, these mini-cabinets are sold on a DYNAMIC LOUDSPEAKER large scale, beca incertain conditions, smallness is BACKGROUND OF THE INVENTION This invention relates to a loudspeaker cabinet and is particularly applicable to a cabinet for a dynamic loudspeaker.

The cabinet, because of its novel provide important advantages, ous constructions, as .regards cabinet and the cabinet.

Some loudspeaker cabinets, known as compact cabinets, can be closed on all sides, filled with cottonwool or the like and can be usually equippedwith several loudspeakers, the frequency range of the cabinet being divided by frequency dividers into low tones, medium tones and high tones.

Such cabinets have numerous disadvantages, for example: only one side of the loudspeaker diaphragm is effective; the efficiency of the cabinet is low; a standard straight "frequency curve is, in practice, scarcely or never achieved, because'the overlaps .of the separate frequency curve portions are added either to form curve peaks or curve troughs which resemble resonance points; even the best frequency switches also construction, may as compared with previthe dimensions of the quality of the tone reproduced by the change the frequency pattern; deviations in the manufacture of cabinets are unavoidable and as a consequence it is very diflicult, to produce a number of cabinets, the quality of which cabinets is consistent throughout the number produced. inconsistencies between cabinets can be noticed by ear if a number of such loudspeakers are compared by means of quick switching over during amusic transmission.

in addition, compact cabinets, in the low bass region, have a distortion factor-up to thirty times greater than HiFi" instruments. In addition, compact cabinets require large'final' amplifier outputs, [in order 'constand to transit to some extent the high-losscorrectly bent frequency curve. Since it is only possible to control amplifiers with abouthalf the nominal output, for

example the doubling of the music output from a compact cabinet would require a normal output of an amplifier.

A large number of sources of errors and disadvantages would be able to be improved or avoided if a single high quality loudspeaker could be installed within a cabinet, instead of having separate loudspeakers for low, medium and high frequency ranges. With mini-cabinets, which are bought on a particularly large scale because little space is available in modern dwellings, it would be particularly advantageous for the cabinet to contain only one loudspeaker. However, the smaller mini-cabinets are made, the more numerous are their disadvantages due to their small physical size,

the poorer their eflrciency becomes and the weaker their bass volume becomes since, with extremely small cabinets, it is solely the rigidity of the enclosed air together with the mass of the vibrating diaphragm which determines the lower frequency limit of a particular cabinet. Consequently, in a very small cabinet, the loudspeaker diaphragm is sometimes made artificially heavier, in order that the diaphragm may radiate 6 low bass notes. For example, a diaphragm which could radiate a genuine 30 c/s, without artificial weighting,

would have to have a diameter of more than half a mequadruplication of the v more important than total quality. Actually, a person quickly becomes accustomed to the tone of a small cabinet and is only disturbed, concerning the tonal quality of the cabinet, when he hears other and better instruments.

Reflex cabinem are also known, which have a window of certain area and depth somewhere in a cabinet wall. The window provides a phase reversal for vibrations of the rear side of the loudspeaker diaphragm and thus facilitates the use of both sides of the diaphragm for the production of sound in a forward direction. The mode of operation of the window is often explained by an electrical equivalent circuit diagram consisting of vcapacitancei, self-inductances and ohmic resistances.

Resistance, capacitance and self-inductance, in series, represent, respectively, mass, elasticity and radiation resistance of the cabinet. Therear side output of the loudspeaker diaphragm is'tumed, by capacitances and inductances (cabinet and window volumes), through 90 180 and activated with the resistance of the operating window volume as radiation resistance.

Such reflux cabinets can have cabinet volumes of from 30 to 500iliters and windows having areas up to 900 cm; they can transmit frequencies down to 20 c/s. Inultra-small forms, theymight have volumes in the region of 20 liters and still be able to transmit a frequency of c/s. However, bass reflex cabinets have a tendency to boom and give booming bass tones. This disadvantage can be weakened by local damping measures, to the disadvantage of the total efficiency of the cabinet, for example by the window of the cabinet being closed with waste material and byproviding loose cottonwool asa lining around the loudspeaker diaphragm basket. The cabinet can thus be improved with regard to bass fi'equencies whilst making it worse in other respects. However, also development possibilities are obtained fi'om the pitch.

0n the other hand, reflux windows have undisputed advantages: the total efiiciency is considerably in-, creased; a balancing of the diaphragm acceleration favors a more uniform soundradiation; and the'production of the bass humps of the sound pressure curve facilitates the radiation of bass tones.

DISCUSSION OF THE DISCLOSURE According to the present invention, there is provided a loudspeaker cabinet comprising:

a fi'ont wall defining a sound aperture;

a rear wall'arranged opposite said front wall; a plurality of side walls joining said front and rear walls; a partition arranged behind said front wall, said partition defining a further sound aperture and having edges which bear acoustically and tightly against an opposite pair of said sidewalls, said edges being shorter in length than said opposite pair of side walls such that other edges of said partition are free within said cabinet;

a loudspeaker means carried by said partition;

spacing means arranged between said front wall and said partition such that said front wall and said partition 5 define an annular gap about the rims of said sound foam material disposed within said cabinet to define at least one damping wall and at least onedamping chamber within said cabinet.

The bracing means may extend between two opposite ones of said side walls, or may extend between said rear wall and said loudspeaker means.

Preferably, the bracing means may extend between said opposite ones of said side walls and also between said rear wall and said loudspeaker means.

In one embodiment, said other edges of said partition are the edges of opposite end regions of said partition and said end regions are deformable within said cabinet, said cabinet further comprising tensioning means accessible externally of said cabinet for deforming said end regions of said partition, relative to said front wall.

In the above one embodiment, preferably said end regionsof said partition can be deformed by said tensioning means such that the minimum distance between at least one of said end regions and said front wall can be'adjusted to a value in the range from zero to 1.7 times the extent of said minimum distance in the undeformed condition of said end regions.

.The bracing means may be a rib arranged on the edge of said rear wall, or, may be a T-shaped member.

Preferably, said foam material is at least partly supported by said bracing means.

The foam material may be in the form of plates providing several damping walls parallel to internal surfaces of'said walls of the cabinet, and may bearranged to form a plurality of rectangular damping chambers of different sizes and shapes. Preferably, said plates extend within said cabinet such that edges of said plates are disposed at a distance from the internal surfaces of at least some of said walls of said loudspeaker cabinet.

The foam material may be in the form of at least one plate having two edges thereof stuck onto one of said walls of said cabinet such that said at least one foam plate forms a tunnel on said one of said walls of said cabinet. Preferably, said one of said walls of said cabinet may be the rear wall of the cabinet.

In addition, it may be advantageous for said at least one plate to extend within said cabinet such that edges thereof other than said two edgesare disposed at a distance from the internal surfaces of at least some of said walls of said cabinet other than said one of said walls.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

FIG. 1 shows a typical curve path of a high-power loudspeaker;

FIG. 2 is a diagrammatic drawing of a straightening of a frequency curve by means of increasing the mass of the diaphragm of a loudspeaker;

FIG. 3 is a crosssectional view of a cabinet having an annular gap;

FIG. 4 is a rear view of the cabinet of FIG. 3 with its rear wall removed;

FIG. 5 is a perspective view of an arrangement of foam plates supported by cabinet bracing means;

FIG. 6 is a perspective view of a tunnel-shaped foam plate; and i I 4 FIG. 7 is a perspective, view of a tunnel-shaped foam plate arranged over a rear wall stiffening rib.

DETAILED DESCRIPTION OF DRAWINGS FIG. 1 shows the characteristic curve of a highpower loudspeaker having an ultra-light diaphragm, low natural frequency and high natural damping, the loudspeaker being housed in a cabinet relieved of air rigidity by its having an internal gap connecting the interior of the cabinet to the external atmosphere. The full-line curve J is a typical impedance double increase (proportional to sound pressure) of an ultra-light, highly damped diaphragm, and the broken line curve b is the associated acceleration curve in the bass region: uniform acceleration shows uniform radiation. The natural resonance at about 70 to 80 c/s has disappeared completely beneath the bass humps.

FIG. 2 shows diagrammatically a frequency curve correction by artificial increase the mass of the diaphragm of a loudspeaker. The curve a relates to a loudspeaker-having low damping and the curve b to a loudspeaker having stronger damping; the curve c is provided by a diaphragm made artificially heavy. The hatched region therefore shows the power loss caused by the artificial weighting of the diaphragm which, in addition, does not provide any lengthening of the curve towards its bass end, but only a certain flattening and decrease in resonance.

FIG. 3 shows a cross-section through a loudspeaker cabinet utilizing the present invention. Between a louds er 1 and a front wall 2 of the cabinet, the front wall 2 having a sound aperture 4, a partition 6, also having a sound aperture, (not shown in detail) is mounted internally on spacing means in the form of spacer rollers 5. By means of screws 8, the loudspeaker 1, the partition 6 and the spacer rollers 5, are fixed on the front wall 2, so that a narrow gap 7 is provided which is in the form of an annulus at the rims of the. sound'apertures in the front wall 2 and in the partition 6. The partition 6 can be deformed by tensioning means in the form of screws 9, so that the cross-sectional area and the volume of the gap 7 are adjustable and a constant acoustic effect can be obtained in series construction. a

The smallest diameter of the sound aperture 4 in the front wall 2 is a few per cent smaller (e.g. 10 per cent) than its largest diameter and than the aperture in the partition 6. Thus, a mixed pressure expulsion chamber 10 is formed, which is supplied both from the front surface of the diaphragm of the loudspeaker l and, through the gap 7, from the rear surface of that diaphragm. The expulsion chamber 10, with strengthened radiation resistance (because it is filled with approximately twice the diaphragm travel volume) and best presence, is the region of contact between the loudspeaker 1 and a hearing room (usually constructed as a pressure chamber) wherein the cabinetisdisposed.

The mixing pressure chamber effect can be supplemented by provision of suitable sound aperture linings (for example: bar gratings; slotted holes; metal gratings; etc.) and by increasing the speed transformation (by changing the percentage of the reduction of The sound pressure increase at the region of entry of sound into the room causes filling of the room with sound without so-called hole character of the tonal image. It produces the sound freely in the room.

Due to the gap 7, theoretically double the stroke volume of the diaphragm, and thus double the sound pressure, emerges from the sound aperture in the front wall 2, substantially without the lack of linearity which can occur with extreme diaphragm displacements.

The gap 7 permits the development of a physiologically pleasing transparent bass tone spectrum with cabinets down to mini-cabinets of 3.6 liter capacity, the gap 7 automatically acting correctly.

A bracing'means in the form of a T-shaped member 12 extends from the rear of the loudspeaker 1 to a rear wall 3 of the cabinet. The member 12 rigidly braces the front and rear walls 2 and 3 of the cabinet to one another, the rigid frame of the loudspeaker 1- thereby being maintained substantially rigid and neutral as regards vibration in the cabinet. This is because the amplitudes of vibrations of the front and rear walls 2 and 3 are always in opposition, so that the frame of the loudspeaker I undergoes substantially no vibrations itself, whether by natural impulses, or whether by concurrent vibration of the cabinet.

The cabinet contains a number of plates 14 of foam material which act as damping walls for standing waves within the cabinet. The plates 14 may be of a soft foam or hard foam material, such as material known under the trade name Moltopren. The arrangement and action of the plates 14 will be described hereinafter, in more detail, with respect to FIG. 5.

FIG. 4 is a rear view of the cabinet of FIG. 3 with the rear wall 3, and the foam plates 14, removed. The vertical longitudinal edges of the partition 6 are in acoustically impervious contact with the inside surfaces of a pair of opposite side walls of the cabinet and are shorter than the inside height of the cabinet. There is thus established an acoustic connection between the rear side of the diaphragm of the loudspeaker 1 and the gap 7 (not visible in FIG. 4) by means of windows which are defined by the free edges of the partition 6 and the surfaces of the top and bottom walls of the cabinet. The loudspeaker 1 is secured to the partition 6 by screws 8. The two vertical side walls of the cabinet are mutually braced by the transverse member of the T- shaped bracing member 12. A stern of the member 12, which stem extends at a right angle to the transverse member to make up the T-shaped member, is secured between the rear wall 3 of the cabinet and the loudspeaker I and presses the loudspeaker against the partition 6, as may be seen from FIG. 3.

FIG. 5 shows, in its left-hand part, that the T-shaped member 12 serves simultaneously as a support for the vertical ones of the foam plates 14 of FIG. 3, which plates are glued to the transverse member of the member 12. The stem of the member 12 is also provided with plates 14, as shown in the right-hand part of FIG. 5. It is to be understood that the right-hand part of FIG. 5 serves to illustrate an example of a cabinet in which the plates stuck to the stem of the member 12 extend vertically within the cabinet, not horizontally as shown in FIG. 3.

It is important that all the plates 14 terminate short of the walls of the box, as is shown in FIG. 3. This obviates standing waves between opposite walls at a most effective point, i.e., in the free air space.

The plates 14, if disposed perpendicularly to the walls of the cabinet, absorb only standing waves whose disturbing effect also occurs only perpendicularly between the walls. The plates 14 may be repeated at each standing wave path, and in fact with different spacings from one another, so that large groups of wave bulges are damped. 4

The overall pattern of this box structure of damping plates can be compared with an arrangement of baffle plates in a fuel tank truck or a tanker, which permits any movement and any discharge of fuel but which quells dangerous splashing. This splashing is analogous to the phenomenon of standing waves in a loudspeaker cabinet.

The frequencies of the standing waves, which are to be damped by the plates 14, can be mathematically represented by a sum under a square root of squares of the length multiples of the cabinet dimensions. The standing waves are a complex, infinite group of disturbing frequencies which are perpendicular to the walls of the cabinet and which can be cancelled out by selective damping. The dimensions, adapted to the diaphragms, bring with increased certainty groups of standing wave bulges effectively into the damping regions of the previously described repeated damping plates 14 the edges of which stand freely in the cabinet. The previously used cottonwool filling, which damped everything without distinction, is here superseded by an intentional selective damping without the actual purpose of the interior of the cabinet, for frequency formation and shaping, .being disturbed. The high tonal regions remain free, clear and unweakened. Even the frequencies which are above the limit of audibility and their summating and differentiating tones (recognizable by a change in sound with turning of only of this ultra-audible range) are freely radiated and are no longer suppressed in the former cottonwool packing. As shown in FIG. 6, in the case of smaller cabinets, the foam plates may be tunnel-shaped and adhesively secured to walls of the cabinet by two edges.

FIG. 7 shows the rear wall of a larger cabinet which is provided, along its longitudinal center line, with a wooden rib 11 which is on edge and which, on screwing the rear wall on to its cabinet, presses tightly against the back of the loudspeaker and thus braces the front and rear walls of the cabinet as does the T-shaped member of FIG. 3. A tunnel-shaped foam plate 13 is disposed over the rib l l on the rear wall of the cabinet and is adhesively secured to the rear wall by its longitudinal edges. When the rear wall is secured to its cabinet and the rib l1 presses tightly against the loudspeaker, the tunnel-shaped plate 13 is pressed flat at a region which is sandwiched between the back of the loudspeaker and the rib 1 1.

Cabinets of different sizes require, for best results for different cabinet sizes, correspondingly different cabinet shapes.

For cabinets of capacities from 25 to 50 liters, predominantly more shallow (from front to rear walls) rectangular cabinets are necessary acoustically, while for mini-cabinets of 15 to 3.6 liters, on the other hand, narrow, deep, cabinets are acoustically necessary. Such a mini-cabinet is shown in FIGS. 3 and 4. A minicabinet should have a rectangular front sound wall, the internal length of which is, at a maximum, three diaphragm diameters, the internal width of the front sound wall being, at a maximum, equal to two diaphragm diameters. Also, for cabinets of capacities from 25 to liters, the depth dimension (from front wall to rear wall) is to be the predominate. A ratio of 3:4 would be suitable for the width to length ratio of the front wall of such a cabinet, a ratio of 1:1 would be unsuitable.

An example calculated on the basis of a cabinet of forty liters capacity, and having a gap defined by its front sound wall and partition, set up in a room of four times four meters (natural frequency 44 c/s), produced, according to Poissons calculation diagramcan 1;, (lowest frequency) of 45 c/s; a window area of 75 cms defined between a free edge of the partition and the adjacent top or bottom cabinet wall, and a gap depth of 5 centimeters between the partition and the front wall of the cabinet. By adjustment of the tensioning screws which can alter the width of the gap and therefore alter the flow resistance of the gap, the difficulties occurring due to relatively great reduction of the cabinet dimensions can be avoided with minimal losses. Considering the electrical equivalent circuit of the cabinet, the capacitative and inductive effect of cabinet and gap-air dimensions is compensated for by an ohmic resistance. By this means, a high-power loudspeaker, as is below described, can be installed to advantage both in the cabinet of the example just considered and in a mini-cabinet.

A suitable, high-power, loudspeaker is one having a lowest possible natural resonance (at the present time, this can go down to 5 c/s). Preferably the loudspeaker has: an extremely low restoring force, limited solely by guarantee of the rest position and gravitational force; large movements in homogeneous and strong magnetic field; high pneumatic and electro-magnetic attenuation in a broad, low, gap; small ohmic values with high impedance, so that two merging bass humps cause a raising of the sound pressure curve. The lower loudspeaker frequency 1",, can be proportional to the natural frequency of the cabinet in which it is installed, multiplied by a root value, in which appears the reciprocal value of the cabinet volume.

In order to design a mini-cabinet, for example of 3.6 liters, the basis is the dimensions of a conventional cabinet of normal size, and namely the diaphragm travel volumes (for a diaphragm travel of 1 mm.) which are proportional to the diaphragm surfaces and are the basis for the sound pressure. If a large cabinet with a diaphragm of 19 cm diameter provides watts, then for the required 8 watts, a diaphragm diameter of about 7.5 cm is to be used. The front wall of the mini-cabinet (maximum dimensions 3 D times 2 D) will consequently be approximately 21 times 12 cm to 15 cm. The largest possible depth desirable for the cabinet is obtained from the cabinet volume of 3.6 liters as about 19 cm (with 11 to 12 cm front width).

The area of the gap 7 for a mini-cabinet produced from the ratios between diaphragm areas and slot areas, and likewise the gap widths are obtained from the ratio between travel volume and the slot volume.

. This rough planning of the dimensions is finely tuned to the maximum readiness for formation of bass humps of the loudspeaker system being used and the best f,,.

With a reduction in the size of the cabinet to form a mini-cabinet, the adjustable slot width 7 takes over as ohmic brake the measurement of the air rigidity. Small, closed, cabinets, with their high air rigidity, make a constant diaphragm acceleration impossible. By the measured slot opening, the internal air mass of the cabinet is unstifiened to conform to the bass and the slot volume is varied. By this means, optimum high power loudspeaker systems with ultra-light diaphragms or in curvi-linear form or consisting of titanium or the like can be used in these cabinets and these diaphragms, also with the small cabinets, still provide their readiness for utilizing their two bass humps for a desired raising of the bass and for suppressing the f,,.

It is important that, instead of the hitherto usual increase in size of the moving masses (diaphragms, oscillating coil, suspension part) which impair the efficiency, the true bass readiness of the high power loudspeakers with ultra-light diaphragms is used.

intensification of the sound radiation is obtained by a combination of the following features: by the provision ,of an annular slot 7 in front of the loudspeaker diaphragm, of which the acoustic energy enters a mixing pressure chamber 10; by the damping of the standing waves without appreciable loss of damping of the acoustic energy; by the full utilization of the air masses vibrating in the cabinet, on the basis of the vibrationfree bracing of the cabinet; and, finally, by the inertial attachment of the loudspeaker.

These improvements in radiation have been confirmed by measurements and by hearing tests, of hearing and illusion, down to the smallest cabinet constructions. It has been further confirmed that the reduction to conform to the bass of the rigidity of ultra-light diaphragm loudspeakers by retaining the bass hump effect is positively honored and can be adjusted to an optimum value. It has been confirmed that mini-cabinets, giving good results, can be made having capacities as small as the capacities of violin bodies. The minicabinet that has been described hereinbefore is a compact cabinet having a window but, except with the large constructions, it is not a reflex cabinet in the conventional sense.

The invention is based on the two basic principles (compact and reflex construction), which have been described hereinbefore, and follows the principle; as far as possible mass-free elasticities and as far as possible non-elastic masses.

1 claim:

1. A loudspeaker cabinet comprising:

a front wall defining a sound aperture;

a rear wall arranged opposite said front wall;

a plurality of side walls joining said front and rear walls;

a partition arrangedbehind said front wall, said partition defining a further sound aperture and having edges which bear acoustically and tightly against an opposite pair of said side walls, said edges being shorter in length than said opposite pair of said walls such that other edges of said partition are free within said cabinet;

a loudspeaker means carried by said partition;

spacing means arranged between said front wall and said partition such that said front wall and said partition define an annular gap about the rims of said sound apertures;

bracing means bracing a pair of opposite ones of said walls; and

foam material disposed within said cabinet to define at least one damp g wall and at least one damping chamber within said cabinet.

2. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means extends between two opposite ones of said side walls.

3. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means extends between said rear wall and said loudspeaker means.

4. A loudspeaker cabinet as claimed in claim 3, wherein said bracing means extends between said opposite ones of said side walls.

5. A loudspeaker cabinet as claimed in claim 1, wherein said other edges of said partition are the edges of opposite end regions of said partition and said end regions are deformable within said cabinet, said cabinet further comprising tensioning means accessible externally of said cabinet for deforming said end regions of said partition relative to said front wall.

6. A loudspeaker cabinet as claimed in claim 5, wherein said end regions of said partition can be deformed by said tensioning means such that the minimum distance between at least one of said end regions and said front wall can be adjusted to a value in the range from 0 to 1.7 times the extent of said minimum distance in the undeformed condition of said end regions.

7. A loudspeaker cabinet as claimed in claim 1, wherein said sound aperture defined by said partition is concentric with said sound aperture defined by said front wall, said sound aperture defined by said front wall being frustum shaped and diverging towards said partition, the smallest internal diameter of said aperture defined by said front wall being smaller by a few per cent than said aperture defined by said partition.

8. A loudspeaker cabinet as claimed in claim 7, wherein said few per cent is substantially 10 percent.

9. A loudspeaker cabinet as claimed in claim 1, wherein said cabinet has a capacity greater than 26 liters and has a dimension between said front and rear walls less than its other dimensions.

10. A loudspeaker cabinet as claimed in claim 1, wherein said cabinet has a capacity of less than 26 liters and has a greater dimension between said front and rear walls than between said opposite pair of said side walls.

11. A loudspeaker cabinet as claimed in claim 10 wherein said loudspeaker means has a circular diaphragm, said front wall having a maximum internal length which is substantially equal to three times the diameter of said diaphragm, and said front wall having a maximum internal width which is substantially equal to twice the diameter of said diaphragm.

12. A loudspeaker cabinet as claimed in claim 11, wherein the ratio of said internal length of said front wall to said internal width thereof is substantially 4:3.

13. A loudspeaker cabinet as claimed in claim 11, wherein said internal width of said front wall is substantially equal to the width of said loudspeaker means in the direction of said internal width.

14. A loudspeaker cabinet as claimed in claim 1, wherein said loudspeaker means has a diaphragm and $%s fi%ai 2 %;i t3?h%r% &s%3h%fln"3 ai'i loudspeaker means.

15. A loudspeaker cabinet as wherein said bracing on said rear wall.

16. A loudspeaker cabinet as claimed in claim 4, wherein said bracing means is a T-shaped member.

17. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means are posts.

18. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means are posts.

19. A loudspeaker cabinet as claimed in claim 1, wherein said foam material is at least partly supported by said bracing means.

20. A loudspeaker cabinet as claimed in claim 19, wherein said foam material is in the form of plates providing several damping walls parallel to internal surfaces of said walls of the cabinet, and arranged to form a plurality of rectangular damping chambers of different sizes and shapes.

21. A loudspeaker cabinet as claimed in claim 20, wherein said plates extend within said cabinet such that edges of said plates are disposed at a distance from the internal surfaces of at least some of said walls of said loudspeaker cabinet.

22. A loudspeaker cabinet as claimed in claim 1, wherein said at least one damping wall extends within said cabinet such that at least one edge of said at least one damping wall is disposed at a distance from the internal surface of at least one of said walls of said loudspeaker cabinet.

23. A loudspeaker cabinet as claimed in claim 20, wherein said plates are fitted between nodal points of said bracing means whereat they are completely compressed without bulging.

24. A loudspeaker cabinet as claimed in claim 1, wherein said foam material is the form of at least one plate having two edges thereof stuck onto one of said walls of said cabinet such that said at least one plate forms a tunnel on said one of said walls of said cabinet.

25. A loudspeaker cabinet as claimed in claim 24, wherein said one of said walls of said cabinet is said rear wall of said cabinet.

26. A loudspeaker cabinet as claimed in claim 24, wherein said at least one plate extends within said cabinet such that edges thereof other than said two edges are disposed at a distance from the internal surfaces of at least some of said walls of said cabinet other than said one of said walls.

27. A loudspeaker cabinet as claimed in claim 1, wherein said loudspeaker means is a dynamic loudspeaker means.

28. A loudspeaker cabinet as claimed in claim 1, wherein said foam material comprises at least one of hard or soft foam material.

claimed in claim 3, means is a rib arranged on edge UNITED STATES PATENT OFFICE QERTIFEQATE UF CQREQTEQN Pateht NQ- 3,680,658- DatedAugust' l; 1972 Inventbfls) 1 H lmut Goeckel It is certified thatferror appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Frcnt Page, change the inventor- 's surname at both occurrences from "Goeskel" to--Goeck el--.

Signed and sealed this 9th day of January 1973..

(SEAL) Attesfc:v j

EDWARD MQFLETCHERJR. t ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-105O (10-69) uscoMM-DC 6Q376-P69 {I U.S. GOVERNMENT PRINTNG OFFICE I959 0-356-334 c UNITED STATES PATENT OFFICE v Y CERTIFICATE OF CORRECTION Patent NQ.1 3,680,658 I I DatQdAug'u Q 972 Inventor(s Helmut Goeckel It is, certified thatferro'ir eppears in the above-identified patent and that seidLettersPaten t are hereby corrected as shown below:

Front Page, change the inventorFs surname at both occurrences from "Goeskel" v to'--Goeck el-.

I Signed and sealed this 9th day of Jenuary'1973..

(SEAL) Attesfcz. j

EDWARD MLFLETCHERJR'. I [ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM 5 (10-69) uscoMM-oc 60376-P69 U S. GOVERYNMENT-PRINTING OFFICEZ 9i 0-35633 

1. A loudspeaker cabinet comprising: a front wall defining a sound aperture; a rear wall arranged opposite said front wall; a plurality of side walls joining said front and rear walls; a partition arranged behind said front wall, said partition defining a further sound aperture and having edges which bear acoustically and tightly against an opposite pair of said side walls, said edges being shorter in length than said opposite pair of said walls such that other edges of said partition are free within said cabinet; a loudspeaker means carried by said partition; spacing means arranged between said front wall and said partition such that said front wall and said partition define an annular gap about the rims of said sound apertures; bracing means bracing a pair of opposite ones of said walls; and foam material disposed within said cabinet to define at least one damping wall and at least one damping chamber within said cabinet.
 2. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means extends between two opposite ones of said side walls.
 3. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means extends between said rear wall and said loudspeaker means.
 4. A loudspeaker cabinet as claimed in claim 3, wherein said bracing means extends between said opposite ones of said side walls.
 5. A loudspeaker cabinet as claimed in claim 1, wherein said other edges of said partition are the edges of opposite end regions of said partition and said end regions are deformable within said cabinet, said cabinet further comprising tensioning means accessible externally of said cabinet for deforming said end regions of said partition relative to said front wall.
 6. A loudspeaker cabinet as claimed in claim 5, wherein said end regions of said partition can be deformed by said tensioning means such that the minimum distance between at least one of said end regions and said front wall can be adjusted to a value in the range from 0 to 1.7 times the extent of said minimum distance in the undeformed condition of said end regions.
 7. A loudspeaker cabinet as claimed in claim 1, wherein said sound aperture defined by said partition is concentric with said sound aperture defined by said front wall, said sound aperture defined by said front wall being frustum shaped and diverging towards said partition, the smallest internal diameter of said aperture defined by said front wall being smaller by a few per cent than said aperture defined by said partition.
 8. A loudspeaker cabinet as claimed in claim 7, wherein said few per cent is substantially 10 percent.
 9. A loudspeaker cabinet as claimed in claim 1, wherein said cabinet has a capacity greater than 26 liters and has a dimension between said front and rear walls less than its other dimensions.
 10. A loudspeaker cabinet as claimed in claim 1, wherein said cabinet has a capacity of less than 26 liters and has a greater dimension between said front and rear walls than between said opposite pair of said side walls.
 11. A loudspeaker cabinet as claimed in claim 10 wherein said loudspeaker means has a circular diaphragm, said front wall having a maximum internal length which is substantially equal to three times the diameter of said diaphragm, and said front wall having a maximum internal width which is substantially equal to twice the diameter of said diaphragm.
 12. A loudspeaker cabinet as claimed in claim 11, wherein the ratio of said internal length of said front wall to said internal width thereof is substantially 4:3.
 13. A loudspeaker cabinet as claimed in claim 11, wherein said internal width of said front wall is substantially equal to the width of said loudspeaker means in the direction of said internal width.
 14. A loudspeaker cabinet as claimed in claim 1, wherein said loudspeaker means has a diaphragm and the area of said aperture defined by said partition is substantially equal to the area of said diaphragm of said loudspeaker means.
 15. A loudspeaker cabinet as claimed in claim 3, wherein said bracing means is a rib arranged on edge on said rear wall.
 16. A loudspeaker cabinet as claimed in claim 4, wherein said bracing means is a T-shaped member.
 17. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means are posts.
 18. A loudspeaker cabinet as claimed in claim 1, wherein said bracing means are posts.
 19. A loudspeaker cabinet as claimed in claim 1, wherein said foam material is at least partly supported by said bracing means.
 20. A loudspeaker cabinet as claimed in claim 19, wherein said foam material is in the form of plates providing several damping walls parallel to internal surfaces of said walls of the cabinet, and arranged to form a plurality of rectangular damping chambers of different sizes and shapes.
 21. A loudspeaker cabinet as claimed in claim 20, wherein said plates extend within said cabinet such that edges of said plates are disposed at a distance from the internal surfaces of at least some of said walls of said loudspeaker cabinet.
 22. A loudspeaker cabinet as claimed in claim 1, wherein said at least one damping wall extends within said cabinet such that at least one edge of said at least one damping wall is disposed at a distance from the internal surface of at least one of said walls of said loudspeaker cabinet.
 23. A loudspeaker cabinet as claimed in claim 20, wherein said plates are fitted between nodal points of said bracing means whereat they are completely compressed without bulging.
 24. A loudspeaker cabinet as claimed in claim 1, wherein said foam material is the form of at least one plate having two edges thereof stuck onto one of said walls of said cabinet such that said at least one plate forms a tunnel on said one of said walls of said cabinet.
 25. A loudspeaker cabinet as claimed in claim 24, wherein said one of said walls of said cabinet is said rear wall of said cabinet.
 26. A loudspeaker cabinet as claimed in claim 24, wherein said at least one plate extends within said cabinet such that edges thereof other than said two edges are disposed at a distance from the internal surfaces of at least some of said walls of said cabinet other than said one of said walls.
 27. A loudspeaker cabinet as claimed in claim 1, wherein said loudspeaker means is a dynamic loudspeaker means.
 28. A loudspeaker cabinet as claimed in claim 1, wherein said foam material comprises at least one of hard or soft foam material. 